For saving time and costs but also for safety reasons, it is important to be able to detect the presence of an optically invisible network, and to locate it with precision, without digging the ground or destroying structures, upon later works.
Several methods may be used for carrying out the detection of optically invisible networks.
The electromagnetic detection is the most used method. This electromagnetic detection may be performed using electromagnetic detectors based on the active detection of an electromagnetic signal.
There is known an active detection method which comprises injecting, by means a current generator, an electric signal in an electrically conductive wire associated to the network to be identified and disposed along the plot of the latter, and this via connection casings installed at regular distances along the network so as to serve as access points, and of using an electromagnetic detector arranged to sense an electromagnetic field created by an alternating current circulating in the electrically conductive wire.
It is known to dispose each connection casing inside a technical gallery or a manhole.
The drawback of such an arrangement of the connection casings lies in the fact that access to the inside of a technical gallery, a manhole or a wall box is generally prohibited to the unauthorized public. Thus, injecting the electric signal allowing to detect the concerned network most often requires obtaining an authorization of the owner of the network to be detected in order to access the connection casing and/or unlocking a closing device preventing access to said connection casing by means of a suitable unlocking member. For some type of networks to be detected, the presence of an authorized person to access the connection casing may also be essential.
Consequently, the detection of a network may prove to be difficult when the connection casings are disposed inside of technical galleries, manholes or wall boxes.
In order to facilitate access to the connection casings and hence the detection of optically invisible networks, it may be considered to dispose the connection casings in areas accessible to the public. Nonetheless, such an arrangement of the connection casings could generate degradations thereof thereby preventing any later detection of the corresponding network.